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Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics II tom.h.wilson Department of Geology.

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Presentation on theme: "Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics II tom.h.wilson Department of Geology."— Presentation transcript:

1 Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics II tom.h.wilson Department of Geology and Geography West Virginia University Morgantown, WV Magnetic methods

2 Tom Wilson, Department of Geology and Geography We’ll pick up with Magnetic Methods on Thursday

3 Magnetic polarity reversals on the sea floor provide Tom Wilson, Department of Geology and Geography

4 Charged particles from the sun stream into the earth’s magnetic field and crash into the gasses of the atmosphere

5 Tom Wilson, Department of Geology and Geography Protons and electrons in the solar wind crash into earth’s magnetosphere.

6 Tom Wilson, Department of Geology and Geography Gochioco and Ruev, 2006 We are also interested in local induced magnetic fields

7 Tom Wilson, Department of Geology and Geography Data Acquisition

8 Tom Wilson, Department of Geology and Geography Steve Sheriff’s Environmental Geophysics CourseEnvironmental Geophysics Proton Precession Magnetometers Tom Boyd’s Introduction to Geophysical Exploration CourseIntroduction to Geophysical Exploration Measuring the Earth’s magnetic field water kerosene & alcohol

9 Tom Wilson, Department of Geology and Geography Source of Protons and DC current source Proton precession generates an alternating current in the surrounding coil Magnetic Fields – Basic Relationships

10 Tom Wilson, Department of Geology and Geography Proton precession frequency (f) is directly proportional to the main magnetic field intensity F and magnetic dipole moment of the proton (M). L is the angular momentum of the proton and G is the gyromagnetic ratio which is a constant for all protons (G = M/L = /  sec). Hence -

11 Tom Wilson, Department of Geology and Geography Locating Trench Boundaries Theoretical model Examination of trench for internal magnetic anomalies. actual field data Gilkeson et al., 1986

12 Tom Wilson, Department of Geology and Geography Trench boundaries - field data Trench Boundaries - model data Gilkeson et al., 1986

13 Tom Wilson, Department of Geology and Geography From Martinek Abandoned Wells

14 Tom Wilson, Department of Geology and Geography Locating abandoned wells

15 Tom Wilson, Department of Geology and Geography From Martinek Abandoned Well - raised relief plot of measured magnetic field intensities

16 Tom Wilson, Department of Geology and Geography Magnetic monopoles p1p1 p2p2 r 12 F m12 Magnetic Force  Magnetic Permeability p 1 and p 2 pole strengths Coulomb’s Law Magnetic Fields – Basic Relationships

17 Tom Wilson, Department of Geology and Geography Force Magnetic Field Intensity often written as H p t is an isolated test pole The text uses F instead of H to represent magnetic field intensity, especially when referring to that of the Earth (F E ). Magnetic Fields – Basic Relationships

18 Tom Wilson, Department of Geology and Geography The fundamental magnetic element is a dipole or combination of one positive and one negative magnetic monopole. The characteristics of the magnetic field are derived from the combined effects of non-existent monopoles. Dipole Field Magnetic Fields – Basic Relationships

19 Tom Wilson, Department of Geology and Geography The earth’s main magnetic field

20 The Earth’s magnetic field Tom Wilson, Department of Geology and Geography

21 Location of north magnetic pole Tom Wilson, Department of Geology and Geography

22 Location of north magnetic pole Tom Wilson, Department of Geology and Geography

23 Tom Wilson, Department of Geology and Geography Magnetic Elements

24 Tom Wilson, Department of Geology and Geography Magnetic Elements three orthogonal strength components (X, Y, and Z); the total field strength and two angles (F, d, i); or two strength components and an angle (H, Z, d)

25 Tom Wilson, Department of Geology and Geography monopole vs. dipole Toxic Waste Magnetic Fields – Basic Relationships

26 Tom Wilson, Department of Geology and Geography Magnetic Elements

27 Tom Wilson, Department of Geology and Geography Magnetic Elements

28 Tom Wilson, Department of Geology and Geography Magnetic Elements

29 Tom Wilson, Department of Geology and Geography Magnetic north pole: point where field lines point vertically downward Geomagnetic north pole: pole associated with the dipole approximation of the earth’s magnetic field. The compass needle points to the magnetic north pole.

30 Tom Wilson, Department of Geology and Geography Magnetic Intensity 11/15/2012 Total intensity = 52580nT

31 Tom Wilson, Department of Geology and Geography Magnetic Inclination 11/15/2012 Inclination = o

32 Tom Wilson, Department of Geology and Geography Magnetic Inclination 11/15/2012 Inclination = o

33 Tom Wilson, Department of Geology and Geography Magnetic Declination 11/15/2012 declination = o

34 Tom Wilson, Department of Geology and Geography W Magnetic Declination Today, the compass points about 9 degrees west of GN

35 Declination to the west as in Morgantown rotate compass dial clockwise to the east Tom Wilson, Department of Geology and Geography To the east, rotate to the west

36 Tom Wilson, Department of Geology and Geography Magnetic Elements for your location

37 Tom Wilson, Department of Geology and Geography Today’s Space Weather Magnetic Elements

38 Another site of interest Tom Wilson, Department of Geology and Geography

39 Tom Wilson, Department of Geology and Geography Anomaly associated with buried metallic materials Bedrock configuration determined from gravity survey Results obtained from inverse modeling Computed magnetic field produced by bedrock Introduction to the magnetics computer lab

40 Tom Wilson, Department of Geology and Geography Where are the drums and how many are there?

41 Tom Wilson, Department of Geology and Geography To do list … Hand in your paper summaries today Hand in the gravity lab today. Magnetic papers will be in the mail room tomorrow morning Magnetic paper summaries will be due Tuesday, December 4 th The magnetics lab will be due December 6 th. Stay tuned for specific instructions on this last lab report Continue reading Chapter 7 –


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